Biometry and A-Scans Flashcards
7 cards from real COT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Biometry and A-Scans flashcards as text
Which IOL formula is generally preferred for eyes with axial lengths greater than 26 mm?
Answer: Barrett Universal II
Barrett Universal II performs well across a wide range of axial lengths, including long eyes over 26 mm.
In immersion A-scan biometry, the probe is:
Answer: Submerged in a saline-filled shell over the eye
Immersion technique uses a saline-filled scleral shell to eliminate corneal compression artifacts.
What does the term 'applanation' refer to in contact A-scan biometry?
Answer: Compressing the cornea with the probe
Applanation biometry involves the probe touching and slightly compressing the cornea, which can shorten axial length readings.
The typical ultrasound frequency used in ophthalmic A-scan biometry is:
Answer: 10 MHz
Ophthalmic A-scans use 10 MHz ultrasound to achieve adequate resolution for ocular structures.
Which structure produces the posterior lens spike in an A-scan waveform?
Answer: Posterior lens capsule
The posterior lens capsule generates the second large spike after the anterior lens spike in A-scan.
A patient has a short axial length of 20.5 mm. Which IOL formula is most appropriate?
Answer: Holladay 2 or Hoffer Q
Hoffer Q and Holladay 2 are preferred for short eyes (axial length <22 mm) to minimize prediction errors.
What artifact can cause a falsely low axial length reading on contact A-scan?
Answer: Corneal compression by the probe
Probe compression indents the cornea and shortens the measured axial length, leading to IOL power errors.